A double acting pump, that is, one which ejects fluid on both strokes of the pumping mechanism, is disclosed in Rolsten U.S. Pat. No. 3,583,837 issued June 8, 1971, and in the prior art cited therein. In a pump of this type it is desirable to minimize the numer of moving parts required, the number of packing glands and seals, and to lighten and simplify the construction is all ways possible without impairing the usefulness and durability of the pump.